1. Field of the Invention
This invention relates in general to container closures, and more particularly to a container closure having multiple sealing surfaces and a tamper-evident ring.
2. Description of the Related Art
Various tamper-evident closures have been proposed wherein a threaded cap has a skirt portion with internal threads for connecting the cap to the threaded neck of a container. A security ring is typically formed during molding of the cap and frangible connections are formed after molding by cutting or slitting openings into the closure at the juncture of the security ring and skirt portion. The security ring may be provided with a plurality of circumferentially spaced, inwardly and upwardly extending tabs or fingers integrally connected to the ring. The outer free ends of the fingers are adapted to engage beneath a shoulder or ledge on the container neck below the threaded portion. In this manner, the cap is prevented from being removed from the container until twisted a sufficient distance to break the frangible connection and thereby separate the cap from the ring.
Closures of the above-mentioned type are typically manufactured with medium or high density polyethylene materials through die casting or thermoforming. The materials must be sufficiently resilient and flexible to enable extraction of the male die member from the cavity of the closure despite the presence of the inwardly and upwardly extending fingers. Since the closures are anchored to the container mainly by engagement of the fingers with the shoulder or ledge, the required flexibility and resilience of the closure to enable separation from the die may also enable the closure to be relatively easily removed from the container without breaking the frangible connection between the skirt and the security ring by slipping the closure off the container in a direction parallel with the axis of the container neck. This is particularly disadvantageous since there is no clear indication that the container has been tampered with.
In recognition of this problem, UK Patent Application No. GB 2 039 817 proposes die molding a closure out of relatively rigid plastics material, such as polypropylene. However, the die-molding process itself is relatively time consuming and therefore contributes to an increase in the cost of manufacturing the closure. In addition, the formation of frangible bridges requires a further processing step wherein openings between the bridges are cut or slit at the intersection of the security ring and skirt portion of the closure. The extra processing step requires extra equipment, time, and energy and thereby contributes to the overall cost of the closure.
Other closures are formed in a single piece. As desirable as the one-piece plastic closure may be, there are a number of problems associated with its use. For example, it is difficult to maintain a seal between the closure and container over an extended period of time under various conditions of packing, storing and handling. Once the closure is firmly engaged on the container, whether by threads or some other means, various parts of the closure are under stress because of forces required to effect a seal. These stresses tend to cause cold flow or creep of the closure material and may cause a breach in the seal between the closure and container. This tendency is augmented when the closure and container are subject to internal pressure from carbonated beverages. A plastic material""s tendency to creep is further affected by elevated temperatures, which may result in a breach of the seal and consequential leakage and/or spoilage of the contents.
Even when the closure is sufficient to retain the beverage in a carbonated state, removal of the closure for dispersing the beverage causes seal degradation to the point where the closure cannot retain its prior sealing ability. Consequently, the beverage will lose much of its carbonation in a relatively short period of time and is often discarded before being completely consumed.
Other closure designs depend on adding a different sealing material on the bottom surface of the closure top wall to maintain a seal between the closure and an upper edge of a neck portion of the container. Such designs, which are often used when the beverage in the container is in a carbonated state, frequently require the application of adhesive material or some other bonding means to bond the different sealing material to the bottom surface of the closure top wall. The use of such bonding means requires more steps in manufacturing and assembly, and it also contributes to an increase in closure manufacturing costs. In addition, the adhesive or other bonding material can deteriorate over time, causing the different sealing material to fall out of the closure. Further, the closure must be completely and firmly engaged on the container in order for such a seal to be fully effective.
Moreover, many closure designs fail to address the problems associated with the storage of beverages containing oxygen or oxygen-producing contents, such as found in some alcohol-based beverages. The presence or production of oxygen can lead to spoilage of the beverage or and a shorter shelf life than beverages without the oxygen content.
In addition to the above drawbacks, the internal threads in prior art closures are typically symmetrical in cross section. Although this construction may facilitate attachment of the closure to the container, the internal threads may not properly seal against the external threads of the container. Moreover, the molding process for closures with threads of this nature typically requires the core mold to be rotated or unscrewed from the interior of the closure after closure formation. This is a time consuming process and is much less efficient than if the core mold were to be withdrawn from the formed closure without rotation.
According to the invention, a closure is provided for connection to a container. The container typically has a neck portion and an external helical thread formed on an outer surface of the neck portion. The closure comprises an upper wall with a lower surface and a skirt formed integrally with and extending generally downwardly from the upper wall. The skirt has a skirt inner surface with an internal helical thread formed thereon for engaging the external helical thread of the neck portion to thereby secure the closure to the container. An inner annular seal extends generally axially downwardly from the upper wall to sealingly engage an inner surface of the neck portion. The inner annular seal has an inner seal apex area and a downwardly sloped surface extending generally downwardly and away from the upper wall to the inner seal apex area. A gas barrier seal has an annular sealing bead positioned between the inner seal apex area and the upper wall inner surface for sealingly engaging the inner surface of the neck portion. The downwardly sloped surface of the inner annular seal holds the annular sealing bead at least adjacent the lower surface of the upper wall.
Further according to the invention, a closure is provided for connection to a container with a neck portion, an annular shoulder and an external helical thread formed on an outer surface of the neck portion above the shoulder. The closure comprises an upper wall including a lower surface and a skirt formed integrally with and extending generally downwardly from the upper wall. The skirt has a skirt inner surface with an internal helical thread formed thereon for engaging the external helical thread of the neck portion to thereby secure the closure to the container. The internal helical thread comprises a crown spaced from the skirt inner surface, an upper thread surface extending generally upwardly and away from the crown to the skirt inner surface, and a lower thread surface extending generally downwardly and away from the crown to the skirt inner surface. A length of the upper thread surface is greater than a length of the lower thread surface to thereby form an asymmetrical cross sectional thread shape. The upper thread surface is adapted to sealingly engage a lower surface of the external helical thread when the closure is installed on the neck portion. An outer annular seal is formed on the inner skirt surface and extends generally radially inwardly toward a central axis of the closure for sealingly engaging the outer surface of the neck portion. An inner annular seal extends generally axially downwardly from the upper wall to sealingly engage an inner surface of the neck portion. The inner annular seal has an inner seal apex area and a downwardly sloped surface. The downwardly sloped surface extends generally downwardly and away from the upper wall to the inner seal apex area. A thickness of the neck portion between the inner and outer annular seals is greater than a distance between the inner and outer annular seals before installation of the closure on the container. The outer annular seal exerts inward radial pressure on the outer surface of the neck portion and the inner annular seal exerts outward radial pressure on the inner surface of the neck portion when the closure is installed on the container. A gas barrier seal is constructed of an elastomer material and comprises an annular sealing bead integrally formed with an annular sealing flange. The annular sealing flange extends generally radially outwardly from the annular sealing bead. The annular sealing bead is positioned between the inner seal apex area and the lower surface of the upper wall for sealingly engaging the inner surface of the neck portion. The downwardly sloped surface holds the annular sealing bead at least adjacent the lower surface of the upper wall. The annular sealing flange has an outside edge positioned near the skirt inner surface and above the upper surface of the outer annular seal. An upper surface of the outer annular seal is adapted to hold the annular sealing flange at least adjacent the lower surface of the upper wall. A tamper-evident security ring is connected to a lower end of the skirt. The security ring comprises an annular wall, and a plurality of circumferentially spaced retaining tabs having a first end resiliently connected to the annular wall through an integral hinge and a second free end extending away from the integral hinge toward a central axis of the closure. Installation of the closure on the neck portion causes the retaining tabs to elastically deflect toward the annular wall when the second free ends pass by the shoulder. The second free ends are adapted to bias against the outer surface of the neck portion below the annular shoulder when the closure is installed on the neck portion.
These and other features and advantages of the invention will become apparent upon reference to the following detailed description and the accompanying drawings.